(1) Field of the Invention
This invention relates to a motor driving apparatus, and more particularly relates to a motor driving apparatus which controls rotation speed of motor according to the pulse width modulation (PWM) signal.
(2) Description of the Prior Art
The technology of using PWM signals to control the rotation of motor is broadly applied to DC motor driving circuit. This technology adopts the PWM signal with a frequency much higher than the rotation speed of DC motor. With the duty cycle of the PWM signal being varied, the charging period for the coil on the rotor can be adjusted so as to control the rotation speed of the motor.
There are two important issues for the design of DC motor driving circuit. Firstly, as the motor is idle for a significant time period, the driving circuit should be able to enter the standby mode for reducing power consumption. Meanwhile, the driving circuit should be able to response the suddenly start-up signal in time. Secondly, the driving circuit should be able to recognize whether the rotor of the motor is locked or not so as to prevent over-charging from damaging the driving circuit.
As to the former, a typical method is to calculate the lasting time the PWM signal stays at low level to judge whether the standby mode should be activated. That is, after the PWM signal has stayed at low level over a predetermined time period, the DC motor driving circuit will enter the standby mode immediately for reducing power consumption.
As to the latter, a typical method is to apply a special control for the motor driving circuit when the rotor is locked. For example, as the motor stops rotation over a predetermined time has been detected, a pulse signal with a predetermined time interval is used to drive the motor instead of the original PWM signal. The pulse signal is capable to have the motor back to normal when the obstacle of the motor is removed.
The rotational condition of motor is determined by the hall signal of the motor. Thus, the lock protection function can be activated according to the hall signal. On the other hand, the control of standby mode is determined according to the lasting time the PWM signal stays at low level. However, the condition that the motor is locked and standby mode are confusing because in both cases the motor is stopped. Thus, how to cooperate the operations of lock protection and standby mode control is an important issue for the skill.